1. Field of the Invention
The present invention relates generally to an antenna for a mobile communication terminal such as a mobile phone, and in particular, to a dual antenna capable of controlling radiation characteristics in a mobile communication terminal. The mobile communication terminal, preferably, a folder type (or dual-LCD (Liquid Crystal Display) folder type) mobile communication terminal, has two directional antennasxe2x80x94one is mounted on a folder and another on a body of the mobile communication terminal such that the radiation characteristics are separately controlled in a suspended state where the folder is folded toward the body and a call state where the folder is unfolded away from the body, contributing to an improvement in antenna performance and a reduction in electromagnetic waves that radiate toward a user""s head.
2. Description of the Related Art
In general, a mobile communication terminal employs an omni-directional, retractable antenna to support duplex transmission and secure portability. A conventional mobile communication terminal has two separate antennasxe2x80x94one is used in a suspended state and another in a call state. The antennas are designed to easily receive and transmit linearly polarized signals. Typically, a spring-shaped helical antenna is mounted on an upper end of the mobile communication terminal. The helical antenna is advantageous in that it enables a call regardless of the direction in which the mobile communication terminal is placed. Further, a monopole-type retractable whip antenna shows better performance than the helical antenna in a state where the mobile communication terminal (or the whip antenna) stands at right angles to the ground. Ideally, however, it is known that when the whip antenna is kept horizontal to the ground, it cannot receive signals. The isotropic (or omni-directional) helix/whip combined antenna of FIGS. 1 and 2 is mounted on an upper end of the mobile communication terminal, as illustrated in FIG. 3.
FIGS. 4A and 4B illustrate an equivalent circuit of the isotropic helix/whip combined antenna. Since the combined antenna is isotropic, it has the omni-directional radiation characteristics centering on a mobile communication terminal 412 as represented by a circle 411 of FIGS. 4A and 4B, causing radiation of electromagnetic waves toward a head of the user during a call. The isotropic combined antenna has a good radiation characteristic when it is spaced apart from the head of the user. However, when it comes close to the head of the user, an amount of the electromagnetic waves absorbed into the user""s head is increased, resulting in a reduction in antenna performance and an increase in SAR (Specific Absorption Rate) representing a degree of the influence of electromagnetic waves on the human body. Accordingly, mobile phone makers and antenna makers are investing a lot of money and manpower in developing an improved antenna capable of preventing the electromagnetic waves from being radiated toward the head of the user. As an alternative, a scheme for radiating most of the electromagnetic waves at the rear of the mobile phone has been proposed. To accomplish this, a patch antenna or a PIFA (Planar Inverted-F Antenna) antenna is typically mounted on an upper end of the rear side of the mobile phone. The antenna prevents the electromagnetic waves from being radiated in the front of the mobile phone, i.e., toward the human body, resulting in an improvement in call quality and a reduction in SAR when it approach the user""s head. However, when it is spaced apart from the user""s head, the antenna may not properly receive waves from a specific direction, thus deteriorating performance of the mobile phone. In this case, the electromagnetic waves radiated in the front of the mobile phone are deceased, whereas the electromagnetic waves radiated in the rear of the mobile phone are increased. Accordingly, when the user talks over the mobile phone with the phone put in his or her pocket, damages caused by the electromagnetic waves may increase undesirably.
It is, therefore, an object of the present invention to provide a dual antenna capable of minimizing the influence of electromagnetic waves on the human body without performance reduction, by separately controlling two antennas mounted on a mobile phone in a call state and a suspended state.
It is another object of the present invention to provide a dual antenna with improved performance in a folder type mobile communication terminal, wherein two antennas have directivities, i.e. radiate and receive signals, in the same direction to reduce electromagnetic waves radiated toward a user""s head in a call state where a folder is unfolded while the two antennas have directivities in an opposite direction to make the overall directivity omni-directional thus to increasing performance in a suspended state where the folder is folded.
It is further another object of the present invention to provide a dual antenna capable of minimizing the influence of electromagnetic waves on the human body without performance reduction by mounting two patch antennas on the rear of a body of a dual-LCD folder type mobile communication terminal and an outer widow of the dual-LCD folder, respectively.
According to one aspect of the present invention, there is provided a dual antenna capable of controlling a radiation characteristic in a folder type mobile communication terminal. The dual antenna comprises a first directional antenna mounted on a folder of the mobile communication terminal, and a second directional antenna mounted on a body of the mobile communication terminal. In a suspended state where the folder is folded against the body, the first and second directional antennas have directivities in an opposite direction. However, in a call state where the folder is unfolded away from the body, the first and second directional antennas have directivities in the same direction.
Preferably, the second directional antenna is mounted on a rear side of the body of the mobile communication terminal, and the first directional antenna is mounted on an outer side of the folder of the mobile communication terminal.
Preferably, the first and second directional antennas are each comprised of a microstrip patch.
According to another aspect of the present invention, there is provided a dual antenna capable of controlling a radiation characteristic in a dual-LCD (Liquid Crystal Display) folder type mobile communication terminal with a dual-LCD folder and a body. The dual antenna comprises a first directional antenna mounted on the dual-LCD folder, and a second directional antenna mounted on the body. In a suspended state, the first and second directional antennas have directivities in an opposite direction. However, in a call state, the first and second directional antennas have directivities in the same direction.
Preferably, the first directional antenna is a POD (Printed-On-Display) antenna. Further, the POD antenna is mounted on an outer window of the dual-LCD folder.